ASoC: atmel: update atmel SSC with DMA binding

As atmel-ssc can be used with DMA, the documentation should be updated.
Also, a configuration DMA example is given.

Signed-off-by: Richard Genoud <richard.genoud@gmail.com>
Signed-off-by: Mark Brown <broonie@linaro.org>

Documentation/devicetree/bindings/misc/atmel-ssc.txt

@@ -7,9 +7,30 @@ Required properties:
 - reg: Should contain SSC registers location and length
 - interrupts: Should contain SSC interrupt
 
-Example:
+
+Required properties for devices compatible with "atmel,at91sam9g45-ssc":
+- dmas: DMA specifier, consisting of a phandle to DMA controller node,
+  the memory interface and SSC DMA channel ID (for tx and rx).
+  See Documentation/devicetree/bindings/dma/atmel-dma.txt for details.
+- dma-names: Must be "tx", "rx".
+
+Examples:
+- PDC transfer:
 ssc0: ssc@fffbc000 {
 	compatible = "atmel,at91rm9200-ssc";
 	reg = <0xfffbc000 0x4000>;
 	interrupts = <14 4 5>;
 };
+
+- DMA transfer:
+ssc0: ssc@f0010000 {
+      compatible = "atmel,at91sam9g45-ssc";
+      reg = <0xf0010000 0x4000>;
+      interrupts = <28 4 5>;
+      dmas = <&dma0 1 13>,
+	     <&dma0 1 14>;
+      dma-names = "tx", "rx";
+      pinctrl-names = "default";
+      pinctrl-0 = <&pinctrl_ssc0_tx &pinctrl_ssc0_rx>;
+      status = "disabled";
+};